CVE WatchOct 7, 2026

CVE-2025-66376

Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability

CVSS

7.2

High

EPSS

20.2%

p97

KEV

YES

Mar 18, 2026

Exploit Today

0-100

Published: Jan 5, 2026 · Last modified: Oct 7, 2026 · CWE-79

EPSS · 30d

17.3%EPSS · 30 days20.2%

2026-09-172026-10-15

KEV catalog record

Product

Synacor / Zimbra Collaboration Suite (ZCS)

Vulnerability

Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability

Added to KEV

Mar 18, 2026

Remediate by

Apr 1, 2026

Known ransomware use

Summary description

Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability in the Classic UI where attackers could abuse Cascading Style Sheets (CSS) @import directives in email HTML.

Required action

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Notes

https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories ; https://nvd.nist.gov/vuln/detail/CVE-2025-66376

Technical description

Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.

Official references

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